Active chip on carrier or laminated chip having microelectronic element embedded therein

ABSTRACT

A structure including a first semiconductor chip with front and rear surfaces and a cavity in the rear surface. A second semiconductor chip is mounted within the cavity. The first chip may have vias extending from the cavity to the front surface and via conductors within these vias serving to connect the additional microelectronic element to the active elements of the first chip. The structure may have a volume comparable to that of the first chip alone and yet provide the functionality of a multi-chip assembly. A composite chip incorporating a body and a layer of semiconductor material mounted on a front surface of the body similarly may have a cavity extending into the body from the rear surface and may have an additional microelectronic element mounted in such cavity.

BACKGROUND OF THE INVENTION

The present invention relates to microelectronic elements such assemiconductor chips and structures incorporating the same.

Conventional semiconductor chips are fabricated by forming activesemiconductor elements such as transistors and circuits incorporatingthe same on a crystalline wafer as, for example, a silicon wafer. Theactive devices are formed by processes such as epitaxial growth, doping,and the like, so as to form the active devices in a very thin layer,typically a few microns thick or less, on a front surface of the wafer.Additional elements such as conductors and resistors also may be formedon the wafer within the active layer, or in other layers close to theactive layer. The active layer may include numerous sub-layers ofelements. The wafer is further provided with electrically conductivecontacts electrically connected to the components in the active layer.The wafer typically is provided with an inert layer commonly referred toas a “passivation” layer overlying the active layer and covering thefront surface of the wafer, except at the contacts. Such a wafer is thencut into individual semiconductor chips, each of which incorporates aportion of the wafer including appropriate circuits and electricalcontacts connected thereto. Thus, each chip has a front surfacecorresponding to the front surface of the wafer and an oppositely facingrear surface corresponding to the original rear surface of the wafer.The active elements and other functional components are disposed in thethin active layer near the front surface of the chip, and the contactsare exposed at the front surface of the chip. Most of the thickness ofthe chip is occupied by the inert material of the original wafer.

Semiconductor chips typically are mounted on a circuit panel, with thefront or rear surface of the chip facing toward the circuit panel, andextending generally parallel to the face of the circuit panel. The chipmay be mounted as such to a circuit panel. Most often, however, the chipis provided in or on a structure referred to as a chip package. The chippackage may physically protect the chip and may provide conductivefeatures which form interconnections between the contacts of the chipand the conductive elements of the circuit board.

Size is a significant consideration in any physical arrangement ofchips. The demand for more compact physical arrangements of chips hasbecome even more intense with the rapid progress of portable electronicdevices. Merely by way of example, devices commonly referred to as“smart phones” integrate the functions of a cellular telephone withpowerful data processors, memory and ancillary devices such as globalpositioning system receivers, electronic cameras, and local area networkconnections along with high-resolution displays and associated imageprocessing chips. Such devices can provide capabilities such as fullinternet connectivity, entertainment including full-resolution video,navigation, electronic banking and more, all in a pocket-size device.Complex portable devices require packing numerous chips into a smallspace. Moreover, some of the chips have many input and outputconnections, commonly referred to as “I/O's.” These I/O's must beinterconnected with the I/O's of other chips. The interconnectionsshould be short and should have low impedance to minimize signalpropagation delays. The components which form the interconnectionsshould not greatly increase the size of the assembly. Similar needsarise in other applications as, for example, in data servers such asthose used in internet search engines. For example, structures whichprovide numerous short, low-impedance interconnects between complexchips can increase the bandwidth of the search engine and reduce itspower consumption.

Considerable effort has been devoted to reducing the dimensions of chipsand packaged chips in the horizontal dimensions parallel to the frontand rear surfaces of the chip, also referred to as the “X” and “Y”directions, so as to minimize the area of the circuit board occupied bythe chip or packaged chip. So-called “stacked” chip arrangements havealso been employed. In a stacked chip arrangements, plural chips aredisposed one above the other, so that the stack extends in a verticaldirection. Such a stack may be formed by providing multiple chips in asingle package, which is then mounted to a circuit board, or byproviding multiple chip packages arranged so that the chip packages canbe stacked one atop the other. This arrangement minimizes the total areaoccupied by the various chips in the horizontal directions, but adds tothe height or vertical dimension of the assembly, also referred to asthe “Z” direction. A stacked arrangement should provide a simple andeffective way of making the vertical connections between the variouschips. The components which form the vertical interconnections ideallyshould not greatly increase the volume of the assembly.

As a general rule, any assemblage of multiple chips occupies a volume noless than the sum of the volumes of the individual unpackaged chips andoften considerably more. It has long been recognized that the volume ofan individual unpackaged chip, and consequently the volume of anyassembly incorporating that chip, can be reduced by reducing thethickness of the chip. As mentioned above, much of the thickness of anindividual chip is occupied by the inert material of the original wafer.Thus, it is common practice in the art to “thin” chips by removing someof the inert material of the wafer from the rear surfaces of the chips,either before or after the wafer is cut into individual chips. Incurrent practice, some chips are thinned to about 100-200 microns.However, the thinning process cannot be continued without limit. Eventhough the electrically active components of the chip are containedwithin a thin layer at the front surface, the chip still must havesufficient thickness to provide physical stability during handling andprocessing. Moreover, simply thinning a chip does nothing to reduce thevolume occupied by the interconnections between the chip and package orbetween the chip and other chips in a stacked arrangement.

Structures referred to herein as “composite chips” include a body withoppositely facing front and rear surfaces similar to a body of aconventional semiconductor chip and include a separately formedsemiconductor layer bonded to the front surface of the body. Thesemiconductor layer may be a layer which is quite thin as, for example,on the order of 10 microns or less in thickness. Such a composite chipmay be made, for example, by forming an active layer on a front surfaceof a first semiconductor wafer and bonding the front surface of thatwafer to a second semiconductor wafer, also referred to as a “carrierwafer.” The first semiconductor wafer is thinned so as to leave only avery thin semiconductor layer including the active layer in place on thefront surface of the carrier or second wafer, thereby forming acomposite wafer. The composite wafer is then cut into individualcomposite chips. Structures of this nature are used, for example, inso-called “rear-surface illuminated” image sensors. In such a structure,the active components in the semiconductor layer include photosensitivecomponents. The photosensitive components are exposed to light impingingon the surface of the semiconductor layer facing away from the carrieror body. Composite chips can be used, for example, in conjunction withordinary semiconductor chips and can be mounted and packaged in waysgenerally similar to the mounting and packaging of ordinary chips.

Despite all of the effort devoted in the art to mounting and packagingof chips, still further improvement would be desirable.

BRIEF SUMMARY OF THE INVENTION

Once aspect of the invention provides a microelectronic structure whichincludes a first semiconductor chip having a body with oppositely facingfront and rear surfaces and a cavity extending in to the body from therear surface. The first chip desirably has active circuit elementsintegrated with the body disposed in an active layer adjacent the frontsurface. The structure according to this aspect of the invention alsoincludes an additional microelectronic element disposed within thecavity. The structure as a whole preferably defines a substantiallyplanar structure rear surface which includes the rear surface of thefirst semiconductor chip. For example, the first chip may have arearwardly facing cavity floor surface within the cavity and a wallbounding the cavity and projecting rearwardly from the cavity floorsurface to the rear surface of the first semiconductor chip. Theadditional microelectronic element may have a front surface disposedwithin the cavity of the first chip and facing forwardly, toward thefloor surface of the cavity. The structure rear surface may include therear surfaces of the first and second chips, which are coplanar with oneanother. Alternatively or additionally, the structure rear surface mayinclude the rear surface of the first chip and an encapsulant.

The first chip may include vias extending forwardly into the first chipfrom the cavity floor surface. These vias may include relativelylarge-diameter first sections near the cavity floor surface andrelatively small-diameter second sections remote from the cavity floorsurface. The first chip may include active elements in an active layerremote from the cavity floor and close to the front surface of the firstchip. The second sections of the vias desirably extend through theactive layer. Because the second sections of the vias desirably haverelatively small diameter, they can extend between the active elementsof the first chip. Desirably, the active elements of the first chip areprovided over substantially the entire area of the chip, including thearea of the chip overlying the cavity. Structures according to certainembodiments of the invention thus can provide the functionality ofplural chips within the volume which would normally be occupied by asingle chip.

Via conductors extending within the vias can provide connectivitybetween the additional microelectronic element and the first chip. In afurther aspect, the additional microelectronic element may have topcontacts exposed at the top surface of such element and electricallyconnected to at least some of the via conductors in the first chip, andmay also have bottom contacts exposed at the bottom surface of theadditional microelectronic element. The additional microelectronicelement may have vias extending through it and via conductors withinthese vias. As further discussed below, this structure and otherstructures discussed below can provide connectivity through the entirestructure. Structures according to certain aspects of the invention canbe stacked one atop the other.

Yet another aspect of the invention provides a composite chipincorporating a body having front and rear surfaces and a layer ofsemiconductor material incorporating active elements mounted on thefront surface of the body. The body has a cavity extending into it fromthe rear surface, and an additional microelectronic element is mountedwithin the body. The body desirable also has vias extending through itas, for example, in walls surrounding the cavity, and the additionalmicroelectronic element may be electrically connected to thesemiconductor layer by way of these vias. Structures according to thisaspect of the invention can be used, for example, to provide verycompact assemblies with photosensitive functionality.

Further aspects of the invention provide systems which incorporatemicroelectronic structures according to the foregoing aspects of theinvention, composite chips according to the foregoing aspects of theinvention, or both in conjunction with other electronic devices. Forexample, the system may be disposed in a single housing, which may be aportable housing. Systems according to preferred embodiments in thisaspect of the invention may be more compact than comparable conventionalsystems.

Still further aspects of the present invention provide methods ofmanufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of a structure according to oneembodiment of the invention.

FIG. 2 is a diagrammatic plan view of a chip used in the structure ofFIG. 1.

FIG. 3 is a fragmentary, partially sectional diagrammatic view of aportion of the chip shown in FIGS. 1 and 2.

FIG. 4 is a fragmentary, partially sectional perspective view of aregion in the chip of FIGS. 1-3.

FIG. 5 is a fragmentary, diagrammatic sectional view depicting elementsof the structure shown in FIG. 1 during a stage of manufacture in aprocess according to a further embodiment of the invention.

FIGS. 6, 7, and 8 are view similar to FIG. 1 but depicting structuresaccording to further embodiments of the invention.

FIG. 9 is a schematic plan view depicting features of the structureshown in FIGS. 8 and 9.

FIG. 10 is a fragmentary, diagrammatic sectional view depicting anassembly incorporating a plurality of the structures shown in Figs. and9, together with other components.

FIG. 11 is a view similar to FIG. 1, but depicting a structure accordingto yet another embodiment of the invention.

FIG. 12 is a schematic sectional view depicting a structure according toyet another embodiment of the invention.

FIG. 13 is a diagrammatic sectional view depicting a structure accordingto yet another embodiment of the invention.

FIG. 14 is a fragmentary, diagrammatic perspective view depictingportions of a structure according to still further embodiments of theinvention.

FIG. 15 is a schematic depiction of a system according to one embodimentof the invention.

DETAILED DESCRIPTION

A microelectronic structure according to one embodiment of the invention(FIG. 1) includes a first semiconductor chip 20 having a body 22 with afront surface 24 facing in a forward direction, toward the top of thedrawing in FIG. 1, and a rear surface 26 facing in the opposite,rearward direction. Rear surface 26 is generally parallel to frontsurface 24. The directions parallel to front surface 24 are referred toherein as “horizontal” directions, and are also referred to herein asthe “X” and “Y” directions; whereas the directions perpendicular to thefront surface are referred to herein as the forward and rearwarddirections, and are also referred to herein as the “vertical” or “Z”directions. The directions referred to herein are in the frame ofreference of the structures referred to. Thus, these directions may lieat any orientation in the normal or gravitational frame of reference.Body 22 includes active circuit elements schematically represented at 28in FIG. 1. Active circuit elements 28 are disposed in a relatively thinlayer adjacent the front surface 24 of the body. The active circuitelements may include devices such as transistors, diodes and otherelements, and circuits incorporating the same. The sizes of the activecircuit elements are, of course, greatly magnified in FIG. 1 for clarityof illustration. Typically, the active circuit elements have dimensionson the order of a few microns or less.

The active circuit elements are integral with body 22. For example, body22 may be formed from a crystalline material, and the active circuitelements may be formed by processes such as epitaxial deposition on thecrystalline material. Merely by way of example, the chip may be aconventional silicon chip in which the body is formed from silicon andthe active circuit elements include doped silicon epitaxially grown onthe silicone of the body. Alternatively, there may be a distinctcompositional difference between the crystalline material forming themajor portion of the body and the active elements as, for example, wherethe body is formed from sapphire or silicon carbide, and the activecircuit elements are formed from III-V semiconductors such as GaAs, GaN.The active circuit elements are disposed in an active layer 30 adjacentthe front surface 24 of the body. The active layer may include activeelements vertically superposed on one another. The active layertypically also includes numerous passive elements such as conductors,resistors, capacitors, and inductors, and may conductive and insulatingelements defining complex interconnections (not shown) between theactive elements. Body 22 also includes a passivation layer 32 coveringat least the active elements of the chip and typically extending overthe entire front surface. Passivation layer 32 may be formed integrallywith the body as, for example, by growing an oxide or nitride layer, ormay include a discrete layer such as a polymeric dielectric as, forexample, a spun-on polyimide. Some or all of the active elements withinthe chip may be connected directly or indirectly to metallizationexposed at points along the front surface. The metallization formscontacts 34 which can serve to connect the active elements to externalelectrical circuit element. The metallization may be disposed behind thepassivation layer 32 and exposed to the front surface through holes inthe passivation layer, or may extend forwardly through holes in thepassivation as depicted in FIG. 1.

First chip 20 has a cavity 36 extending into the body from the rearsurface 26. The cavity has a rearwardly facing floor surface 38. Body 22defines walls 40 extending rearwardly from floor surface 38 to the rearsurface 26. As best seen in FIG. 2, the walls 40 bound cavity 36 andfloor surface 38 on opposite sides thereof. In the particular embodimentshown in FIGS. 1 and 2, there are four walls bounding cavity 36 on allfour sides and thus completely encircling the cavity. However, in otherembodiments, there are only two walls 40 disposed on two opposite sidesof the cavity. Each wall 40 has an inner surface 42 facing inwardlytoward the cavity 36. The inner surfaces slope in horizontal directionsaway from one another, so that the horizontal dimensions of the cavityincrease in the rearward direction from floor surface 38 to rear surface26. The rear surface 26 is defined by the ends of the walls remote fromthe floor surface 38. Rear surface 26, apart from the cavity, desirablyis generally planar. Body 22 may have a layer of a dielectric, such as apolymeric dielectric 44, covering the crystalline material of the bodyat the floor surface 22.

The cavity, as measured at floor surface 38, may occupy a substantialportion of the area of the chip, typically about 25% or more, and insome cases 50% or more. As used herein, unless otherwise specified, the“area” of a feature of a chip is the area in a horizontal plane. Thus,the area of the cavity can be taken as the area of floor surface 38,whereas the area of the chip can be taken as the entire area of the chipas seen in a horizontal plane, i.e., the total area of front surface 24or rear surface 26, including the area occupied by the cavity and walls.The thickness of body 22, i.e., the distance T_(F) between the frontsurface 24 and rear surface 26, may be selected as desired, buttypically is less than about 200 microns, to provide a relativelycompact assembly. The depth D_(C) of the cavity as measured from floorsurface 38 to rear surface 26 in the vertical direction may be asubstantial portion of thickness T_(F) so that the region of the body 22overlying cavity 36 and floor surface 38 forms a relatively thindiaphragm-like structure extending between the walls 40. The thicknessT_(D) of the diaphragm, as measured between the front surface 24 andfloor surface 28, can be just slightly greater than the thickness ofactive layer 30. For example, t_(d) may be between about 25 microns and50 microns. Walls 40 serve to reinforce the thin diaphragm and constrainthe first chip as a whole against bending in the directions transverseto the horizontal plane of the front surface 24. The materialincorporated in walls 40 provides considerably greater reinforcementagainst such bending than an equivalent volume of material spread as auniform-thickness layer over the entire area of the chip.

First chip 20 has vias 48 extending into the body 22 from the cavityfloor surface 38. As used in this disclosure, the term “via” refers to avertically extensive opening in the material of the body. The viasdepicted in FIG. 1 extend through the diaphragm section of the body andthus extend to the front surface passivation layer 32 and through thatlayer. However, this is not essential; some or all of the vias mayterminate below the front surface passivation layer or within thesemiconductor material of the body itself. The active layer 30 extendswithin the diaphragm section of the chip so that some or all of theactive circuit elements are disposed in the diaphragm portion of thebody and overlie cavity 36. Stated another way, some or all of theactive elements 28 may be disposed so that lines drawn from theseelements in the rearward direction would pass through the cavity. Atleast some of the vias 48 extend into and through active layer 30 andextend between active elements 28. Those regions of vias 48 which aredisposed within active layer 30 desirably are of relatively smalldiameter, preferably less than about 50 microns and more desirably about1 to about 20 microns. This minimizes the area within the active layeroccupied by the vias and thus allows compact placement of the featuresrequired in the active layer, including the active elements and routingconductors. Preferably, each via has a first portion 50 disposedadjacent the cavity floor surface 38 and a second portion 52 extendingwithin the active layer 30, the second portion having a diameter ordimension in the horizontal directions smaller than the diameter orhorizontal dimension of the first portion. The vias and via conductorscan be formed by processes such as those disclosed in greater detail inthe co-pending, commonly assigned U.S. patent application Ser. Nos.12/842,587, 12/842,651, 12/842,612, 12/842,669 and 12/842,717 and inpublished US Patent Application Publication No. 20080246136, thedisclosures of which are incorporated by reference herein. For example,the second portion 52 can be formed by a carefully controlled,close-tolerance process such as reactive ion etching or the like,starting from the front surface of the via; whereas the first portion 50can be formed by a relatively coarse process as, for example, amechanical process such as sandblasting, starting from the oppositesurface of the semiconductor body. The use of such a coarse processallows rapid removal of the material of the body and hence minimizes thecost associated with via formation. In still other embodiments disclosedin the aforementioned applications incorporated by reference herein, thefirst sections of the vias can be formed, and a temporary or permanentlayer applied within the first section can serve as a mask for etchingthe second sections of the vias. Because the first portions 50 lierearwardly of the active layer 30, the area occupied by the firstportions 50 remains available for placement of components within theactive layer. Also, the first portions 50 need not be preciselypositioned to avoid features within the active layer. Either or bothsections of the vias can be formed before or after the processes used tofabricate the structures within the active layer.

A via conductor 54 formed from an electrically conducted material as,for example, a metal such as copper, extends within each via 48. Eachvia conductor 54 terminates in a floor surface connection pad 56 (FIGS.1 and 4) adjacent the floor surface 38. The forward ends of the viaconductors terminate in front surface connection pads 58 adjacent thefront surface 24 of the body. As best seen in FIG. 4, the floor surfacepad 56 of each via conductor is aligned with the first section 50 of thevias, so that the perimeter of the pad 56 lies within the perimeter ofthe via first section 50. In other arrangements, where the pads 56 areof a larger diameter, the pads may overlap the floor surface 38 outsideof the vias to some degree. Pads 58 at the front surface are alsoaligned with the openings of the vias. A liner 59 (FIG. 1) is disposedwithin each via and surrounds the via conductor 54. Liner 59 desirablyis formed from a material, most preferably a dielectric material such asa polymer having a modulus of elasticity lower than the materialconstituting body 22. The polymer of the linings may merge with apolymeric material constituting the passivation layer 32 and the floorsurface passivation layer 44. Floor surface pads 56 are exposed at floorsurface 38 of the cavity. For example, pads 56 may be disposed on theface of passivation layer 44 facing rearwardly or may be buried withinthe passivation layer, but exposed through holes in the passivationlayer. Similarly, front surface pads 58 may be exposed at the frontsurface 24 of the body.

As further discussed in the applications incorporated by referenceherein, the low-modulus dielectric liners mechanically isolate the viaconductors 54 and pads 56 and 58 from the relatively rigid material ofthe body, at least to some degree, and therefore reduce localizedstresses due to the differing thermal expansion and contractioncharacteristics of the via conductors and the body. For example, wherethe via conductors are metallic and have a greater coefficient ofthermal expansion than the body 22, a via conductor which is in contactwith the material of the body will be constrained against expansion inhorizontal directions. The via conductor, therefore, will tend to expandto an even greater degree in the vertical directions when the assemblyis heated as, for example, during operation or during manufacturingprocedures such solder-bonding. This large vertical expansion tends todisrupt the pads and disrupt bonds to other assemblies. By contrast,where the liner is provided, the via conductor can expand and contractradially, and hence the degree of expansion in the vertical direction isreduced. Moreover, because the via conductors and pads are at leastpartially mechanically isolated from the body, the via conductors andpads can move to some extent under the influence of externally appliedloads as, for example, loads applied by other elements bonded to thepads. This tends to reduce stresses in the bonds between the otherelements and the pads.

Terminals 60, suitable for connection to a larger assembly, are providedon the front surface 24 of the first chip 20. In the particularembodiment shown, each terminal includes a metallic pad supported abovethe front surface by a bump or projection 62 formed from a dielectricmaterial. This dielectric material may be of the same composition asfront-surface passivation layer 32, or may be a different material suchas a material having a lower elastic modulus. Terminals 60 may beprovided with bonding metallurgy as, for example, a solder or eutecticbonding material 64.

The terminals 60, via conductors 54, and the elements in the activelayer 30, such as active elements 28, are interconnected with oneanother as required for circuit functionality. For example, some or allof the front surface pads 58 may be connected to some or all of theterminals 60 by traces 66 extending along the front surface of the chipand onto the bumps 62. Also, some or all of the front surface pads maybe connected to active elements 28 by additional traces extending alongthe front surface to contacts 34. Such traces may be formed integrallywith the front surface pads or as separate elements. The traces arereferred to herein as extending “along” the front surface need not be atthe ultimate exposed surface. For example, the traces may be on theultimate exposed surface of the front surface passivation layer 24,within the passivation layer, or between the passivation layer and thebody 22. In a further arrangement (not shown) A via conductor whichterminates rearwardly of the front surface may be connected by traces tointernal components within the active layer, or to other conductivecomponents of the chip.

The assembly further includes a second microelectronic element 70 which,in this instance, is a second semiconductor chip having a body 72 with agenerally planar top surface 74 and an oppositely facing, generallyplanar bottom surface 76. The second chip 70 includes active elements 78disposed in an active layer near the top surface 74. As with the firstchip, the active layer may also include elements such as passivecomponents, conductors and insulators. The second chip may include a topsurface passivation layer 82 at the top surface 74 and electricallyconductive contacts 84 exposed at the top surface 74. The contacts maybe on the surface of passivation layer 82, facing away from body 72, ormay be within or below the passivation layer and exposed throughopenings in the passivation layer.

The second chip 70 is disposed within cavity 36, with the top surface 74of the second chip facing forwardly with respect to the first chip, andhence facing toward the floor surface 38 of the cavity. Contacts 84 ofthe second chip are aligned with and bonded to some or all of the floorsurface pads 58. Thus, the active elements 78 within the second chip areelectrically connected through the contacts 84 and the via conductors 54to the terminals 60 carried on the front surface of the first chip, andare also connected to the active elements 28 and other components withinthe active layer 30 of the first chip.

The contacts 84 of the second chip are bonded to the floor surfacecontact pads 56 of the first chip by any suitable bonding metallurgywhich provides a good physical connection and a good electricalconnection. For example, solder bonding, eutectic bonding, and the likemay be employed.

The bottom surface 76 of the second microelectronic element issubstantially coplanar with the rear surface 26 of the first chip ormicroelectronic element. Stated another way, the thickness of the secondchip or additional microelectronic element, i.e., the distance betweenthe top surface 74 and bottom surface 76, is equal to or slightly lessthan the depth D_(C) of cavity 36. An encapsulant 86 fills the spacewithin the cavity around the second microelectronic element or chip 70,and the encapsulant defines small surfaces 86 substantially coplanarwith the rear surface 26 of the first chip and the bottom surface 76 ofthe second chip, so that the encapsulant and the chips cooperativelydefine a substantially continuous planar surface facing in the oppositedirection from the front surface 24 of the first microelectronicelement.

The first chip 20 desirably has a total thickness T_(F) near the minimumthickness required for physical stability in manufacture and handling.The second chip 70 has a thickness which necessarily is less than T_(F).However, because the second chip 70 is mounted within the cavity, it isphysically protected by the first chip. As discussed below, the secondchip 70 may be thinned to the thickness which it has in the finishedassembly near the end of the manufacturing process, after the secondchip has been mounted within the cavity and secured in place. At thattime, the second chip is physically reinforced by the first chip and bythe surrounding encapsulant. Stated another way, the second chip 70 mayhave a thickness which is less than that which would be required forphysical stability of the second chip, if the second chip was providedas a separate, independent chip. For example, the thickness of thesecond chip may be less than about 100 microns, as, for example, lessthan about 50 microns or about 5 to about 50 microns.

Encapsulant 86 desirably forms a physical bond between the first andsecond chips, so that the second chip is mechanically connected with thefirst chip. This connection need not be rigid. Encapsulant 86 can havean elastic modulus lower than the elastic modulus of the materialconstituting the chips. Moreover, the electrical interconnectionsbetween contacts 84 of the second chip and the floor surface pads 56 ofthe first chip also provide a mechanical connection between the firstand second chips.

Although the encapsulant 86 is shown as separate from the floor surfacepassivation layer 44 and top surface passivation layer 82 and asintervening between these passivation layers, the passivation layers maytouch one another and may be directly bonded to one another as, forexample, where the passivation layers have adhesive properties or can bebrought to a state where the passivation layers bond with one another.In such instance, there may or may not be still be some separateencapsulant around the edges of the chip 72.

The structure as a whole includes the functionality of both the firstand second chips. Because the active elements of the first chip mayextend over substantially the entire area of the first chip, thehorizontal dimensions of the first chip may be same as or minimallylarger than a comparable first chip formed without the vias and viaconductors. Thus, the volume of the entire assembly, including the firstand second chips, may be essentially the same as or only minimallylarger than the volume of a first chip having only the functionality ofthe first chip.

An assembly as depicted in FIG. 1 can be made by forming the activeelements and other components of the active layer 30 on a wafer 120(FIG. 5). At this stage of the process, the thickness T_(W), or distancebetween the front and rear surfaces of wafer 120, desirably is somewhatgreater than the desired thickness T_(F) (FIG. 1) of the first chip inthe completed assembly. The wafer 120 includes numerous regions, each ofwhich will form one of the first chips 20 (FIG. 1) in the finishedassembly. These regions are depicted as separated by boundaries 108 inFIG. 5 for clarity of illustration, but there need not by physicalboundaries present at this stage of the process. After formation of theactive elements and, typically, some or all of the other components inthe active layer at or near the front surface 124 of wafer 120, thefront surface 124 is temporarily secured to a carrier 102 (FIG. 5), suchas an additional wafer or other element having significant physicalrigidity and strength. The wafer 120 may be secured to carrier 102 by atemporary bonding layer 104. Cavities 36 are formed in the rear surfaceof the wafer, preferably by a mechanical technique such as sandblasting.The cavity formation step may be performed before or, more typically,after formation of the active layer and after attachment to the carrier102.

After formation of the cavities 36, vias 48 are completed. The entirevia 48 may be formed at this time. Alternatively, the second portions 52of the vias near the front surface 124 of the wafer may be formedconcomitantly with the formation of the active elements and otherfeatures of the active layer, and only the first portions 50 may beformed after formation of the cavities. As mentioned above, the firstportions 50 may be formed by a mechanical process such as sandblasting.The via liners 59 and the floor surface dielectric layer 44 may beformed by depositing a dielectric material into the cavities 36 and intothe first portion of the vias. Here again, some portions of the vialiners may be formed during the earlier stages of the process if thesecond portions 52 of the vias are formed earlier. The via conductorsand the associated pads 56 at the cavity floor surface (FIG. 1) may thenbe formed. After formation of the via conductors and floor surface pads,the second chips 70 are placed into the cavities 36 and electricallyconnected to the floor surface pads, and the encapsulant 86 isintroduced into the cavities and cured.

Once the encapsulant has been cured, the wafer 120, second chips 70, andencapsulant 86 are processed as, for example, by mechanically grindingthe entire assembly so as to remove material from the rear surfaces ofthe second chips, the wafer, and the encapsulant, and bring the wafer tothe desired thickness of the first chip. This process forms acontinuous, planar rear surface 106, indicated in broken line in FIG. 5.After processing, each region of wafer 120 has a continuous planar rearsurface, as discussed above with reference to FIG. 1, including the rearsurface 26 of the first chip, the encapsulant surface 88, and the bottomsurface 76 of the second chip 70. Following planarization, the wafer 120is removed from the carrier and singulated or cut-apart along boundaries108 between the individual wafers so as to separate the first chips fromone another and form individual assemblies as shown in FIG. 1. Suchsingulation can be performed before or after removal from the carrier.Also, before or after singulation, features such as the bumps 62 andterminals 60 are formed on the front surfaces of the first chips.

The assembly shown in FIG. 6 is similar to the assembly discussed abovewith reference to FIGS. 1-5, except that the thickness of the secondchip 270 is less than the depth D_(C) of the cavity 236 in the firstchip 220. Therefore, the rear surface of the completed assembly consistsof the rear surface 228 of the first chip and the encapsulant surface288 defined by the encapsulant within cavity 236. Assemblies of thistype can be formed by a process similar to the process discussed abovewith reference to FIG. 5, except that the second chip 270 is thinned toits final thickness before placement within cavities 236. In a variantof this process, the wafer used to form the first chips 220 may also bethinned to its final thickness so as to form the rear surfaces 226 ofthe first chips in the wafer before placement of the second chips.Following placement of the second chips, the assembly is treated bytreating the encapsulant as, for example, by treating the encapsulantduring or after placement of the encapsulant within cavities 236. Forexample, the rear surfaces 226 may be engaged with a mold, and theencapsulant may be introduced in a liquid form and molded to form theencapsulant surface 238 coplanar with the rear surfaces 226 of the firstchips. Alternatively, the encapsulant may be filled into cavities 236 soas to protrude beyond the rear surfaces 226 of the first chips, and theassembly may be subjected to a process such as a polishing process usinga relatively soft abrasive which removes the encapsulant projectingbeyond the rear surfaces of the first chips, but which does not removematerial from the rear surfaces of the chips themselves.

The assembly of FIG. 7 is similar to the assembly of FIG. 1, except thatthe second chip 370 has vias 302 extending through it, from its topsurface 374 to its bottom surface 376. Vias 302 are provided with viaconductors 304. The top surface 374 of the second chip is provided withconductive elements such as pads 306 and elongated redistribution traces308. Some or all of these conductive features are connected to thecomponents within the active layer of the second chip as, for example,to active elements 378, and to the via conductors 304 of the secondchip. The bottom surface 376 of the second chip 370 may have terminals310 similar to the terminals 360 formed on the front surface of thefirst chip 320. Here again, the conductive features of the second chip370, including the via conductors 304, are electrically connected to thevia conductors 354 of the first chip 320. These conductive features ofthe two chips may be electrically interconnected with one another asdesired so as to form any desired pattern of electricalinterconnections. The patterns of electrical interconnections mayinclude connections between via conductors 354 of the first chip and viaconductors 304 of the second chip, and may connect some or all ofterminals 360 on the first chip with terminals 310 of the second chip,so as to provide a composite through connection extending entirelythrough the assembly. Some or all of the internal active features of thechips, such as features 328 and 378, can be connected to these throughconductors or to the terminals of the first or second chip. The vias302, via conductors 354 and associated components of the second chip maybe similar to the vias 48, via conductors 54 and associated componentsdiscussed above with reference to FIGS. 1-4. In this case as well, thevias desirably have larger sections disposed rearwardly of the activelayer 378 of the second chip.

Assemblies as shown in FIG. 7 can be fabricated by procedures similar tothose discussed above with an additional step for forming at least thelarger, first sections of vias 302 before or after the second chips 370are united with the first chips 320. For example, at least the larger,first sections adjacent bottom surface 376 of the second chip 370 can beformed after the wafer and second chips are ground or otherwise treatedto form the bottom surface of the assembly. Also, dielectric liners andvia conductors can be formed in vias 302 after assembly of the secondchips to the first chips and desirably after formation of the bottomsurface of the assembly. Assemblies as shown in FIG. 7 can be stackedone atop the other, with the rear surface terminals 310 on one unitaligned with and bonded to the top surface terminals 360 on the nextunit. Such a stacked assembly can be connected to a circuit panel suchas a circuit board by bonding the terminals 310 or 360 on one of theunits to the circuit board.

A structure 400 according to a further embodiment (FIG. 8) is generallysimilar to the structures discussed above. Here again, the first chip420 has a cavity 436 extending into the body of the chip from the rearsurface 426. The first chip has walls 440 bounding the cavity, suchwalls having sloping wall surfaces 442 facing inwardly toward thecavity. Vias 402 extend through the first chip 420, from the frontsurface 424 to the rear surface 426. In this embodiment, the vias extendthrough the walls 440, rather than through the diaphragm section of thechip overlying cavity 436. These vias are provided with via conductors404, pads 413 at the front surface of the first chip and 409 at the rearsurface, the pads being electrically connected to the via conductors. Inthis embodiment, the pads 413 and 409 form terminals suitable forconnection to external elements.

Here again, the cavity has a rearwardly facing floor surface 438. Thefirst chip is provided with a set of redistribution conductors 405extending along the cavity floor surface 438. These redistributionconductors may be in contact with the body of the chip or may be in oron a passivation layer disposed on the floor surface. Redistributionrearward conductors 407 extend along the inner surfaces 442 of walls440. These redistribution rearward conductors are connected to theterminals 409 on the rear surface 426 of the chip. Some or all of therearward redistribution conductors 407 may be connected to the terminals409 and thus connected to via conductors 404. Additional terminals (notshown) which are not directly associated with vias may be provided onthe front and rear surfaces of the first chip, and some or all of therearward redistribution conductors may be connected to the additionalterminals on the rear surface.

The second chip 470 has electrically conductive components such ascontacts 406 on its top surface 474 electrically connected to theinternal components of the second chip. The second chip also hasredistribution conductors 415 extending along the top surface 474. Hereagain, the redistribution conductors may be in or on a passivation layerat the top surface.

The redistribution conductors 405 and 415 are spaced apart from oneanother in a vertical direction and separated from another by theencapsulant 480 within the cavity. Thus, the redistribution conductorsof the two chips can cross one another without contacting one another,or can be connected to one another as by a bonding material applied atthe crossing points. As best seen in FIG. 9, the floor surfaceredistribution conductors 405 of the first chip, depicted in brokenlines for clarity of illustration, extend predominantly in a firsthorizontal direction, referred to herein as the “X” direction; whereasthe redistribution conductors 415 of the second chip extendpredominantly in a second, perpendicular horizontal direction, referredto herein as the “Y” direction. Thus, the redistribution conductors maybe selectively connected to one another by conductive bonds 419 atselected crossing points. In FIG. 9, these conductive bonds areindicated by black rectangles. The floor surface redistributionconductors 415 of the first chip may be continuous with the rearwardredistribution traces 407 extending along the walls. Some of the floorsurface redistribution traces may be provided as short stub tracesextending in the second or Y horizontal direction, these traces beingcontinuous with rearward redistribution traces 407 which also extend inthe Y or second horizontal direction. These stub traces 421 may beconnected by bonds 419 to top surface redistribution traces 415 of thesecond chip.

As in the embodiment discussed above with reference to FIG. 7, some orall of the terminals 406 and redistribution conductors 415 of the secondchip may be connected to the via conductors 454 of the first chip.Moreover, some or all of the redistribution conductors 405 of the firstchip and redistribution conductors 415 of the second chip may beconnected to the rearward redistribution conductors 407 and thusconnected to the through via conductors 404 of vias 402 in the walls ofthe first chip. This arrangement allows extraordinary versatility informing interconnections within the structure. For example, theinterconnections provided by the redistribution conductors can be usedto route signals within one or the other of chips 420 and 470, orbetween these chips.

As shown schematically in FIG. 10, units 400 can be stacked to form acomposite assembly, with the rear surface terminals 409 of one unitbeing connected to the front surface terminals 413 of the next adjacentunit as by solder bonds 431. In the particular arrangement shown, thecomposite assembly is connected to a circuit panel 491 by bonding therear surface terminals 409 of one unit to conductive pads 493 of thecircuit panel. In other arrangements, the front surface terminals 413can be used for connection to a circuit panel.

A further embodiment (FIG. 11) is similar to the embodiments discussedabove, except that the encapsulant 586 within the cavity 536 provides arelatively broad region surrounding the edges of the second chip 570,and vias 502 are formed within this region. These vias are provided withadditional via conductors 504, which provide still further verticalconnectivity. Some of the terminals 510 at the rear surface of thestructure are provided on the surface 588 defined by the encapsulant.The particular structure depicted in FIG. 11 does not have viasextending through the first chip 520. Thus, features 578, such as activeelements in the active layer of the second chip 570, are connected torear surface terminals 510 by the via conductors 504 in vias 502. Floorsurface redistribution traces 505 extending along the floor surface ofcavity 536 in the first chip and top surface redistribution traces 515extending along the top surface of second chip 570 connect the contactsof the second chip to via conductors 504. Additional connectivity toterminals 510 on the rear surface of the structure may be provided byadditional via conductors extending through vias 503 in the second chip570.

In yet another embodiment (FIG. 12), the second microelectronic element670 provided within the cavity 636 of the first semiconductor chip 620is not a simple semiconductor chip. Rather, second microelectronicelement 670 itself is a structure including a second semiconductor chip602 defining a cavity 604 and having a third microelectronic elementsuch as a third semiconductor chip 606 received therein. Any or all ofthe features discussed above can be used in assembly 602. The viaconductors 608 of the various chips may be interconnected with oneanother by conductive bonds 610, as well as by redistribution conductorsextending on the various cavity floor surfaces and on the top or frontsurfaces of the various chips. Some or all of such interconnections mayform continuous conductive paths extending entirely through theassembly, between the front surface 623 and the rear surface 625 of theassembly (the surfaces at the top and bottom of the assembly as seen inFIG. 12). Any or all of the active elements in the active layers of thevarious chips can be interconnected with one another and with terminalson the surfaces of the assembly. This approach can be extended furtheras, for example, to provide a fourth semiconductor chip within a cavityin chip 606. The process for fabrication of an assembly as shown in FIG.12 can be generally similar to those discussed above. Merely by way ofexample, the rear surface of the assembly can be brought to a planarcondition by grinding or otherwise treating the rear surface of thefirst chip and the bottom surfaces of chips 602 and 606 simultaneously,along with the encapsulant contained in the cavities 636 and 604.

A structure according to yet another embodiment of the inventionincludes a composite chip 720 (FIG. 13). The composite chip incorporatesa body 722 which may be formed from a crystalline material as, forexample, silicon, a polycrystalline or partially crystalline materialsuch as alumina, or an amorphous material. Body 722 has oppositelyfacing front and rear surfaces 724 and 726. Body 722 has a cavity 736formed in its rear surface and extending into the body from the rearsurface. The composite chip further includes a semiconductor layer 702bonded to the front surface 724 of body 722. Semiconductor layer 702incorporates active semiconductor elements which are linked by internalconnections (not shown) to conductive elements 704 exposed at therearwardly directed face of layer 702, facing toward body 722. Theseconductive elements, in turn, are connected to electrically conductiveelements 706 extending along the front surface 724 of body 722.Conductive elements 706 may include numerous separate traces or pads.The bond between layer 702 and body 722 is schematically shown as anadhesive layer 708. Alternatively, the layer 702 and body 722 may bebonded to one another by processes such as diffusion bonding, which doesnot involve a separate adhesive layer. In the particular embodimentshown in FIG. 13, some of the active elements 728 include photosensitiveelements such as photodiodes, phototransistors, or photoconductors.Layer 702 has a front surface 710 facing forwardly, away from body 722.The thickness T_(L) of layer 702 is small enough that light impinging onfront surface 710 can pass through the layer to the photosensitiveactive elements 728. For example, layer 702 may be about 15 micronsthick or less, typically about 10 microns thick or less. Layer 702 maybe formed as part of a generally conventional semiconductor wafer whichis considerably thicker than the desired thickness of the layer. Thiswafer may be laminated to another wafer incorporating the material ofbody 722 using generally conventional techniques. After lamination,material is removed from the wafer incorporating the semiconductorelements so as to reduce the thickness of the wafer and form frontsurface 710.

Body 722 incorporates walls 740 extending around and bounding cavity736. Here again, the walls have vias 710 extending through them and viaconductors 712 disposed within the vias. In this embodiment as well,vias 710 may be multi-diameter vias. Thus, those portions of the viascloser to the front surface 724 of the body may be of considerablysmaller diameter than the via portions near the rear surface 726, andthe via conductors 712 may likewise have varying diameters along thevertical extent of the via. Via conductors 712 are electricallyconnected to the conductive elements 706 extending along the frontsurface 724 of the body and thus electrically connected to theconductive elements 704 of the semiconductor layer 702. Via conductors712 are provided with terminals 713 exposed at the rear surface 726 ofthe body.

A second microelectronic element such as a second semiconductor chip 770is disposed within the cavity 736 of the body. Here again, the secondmicroelectronic element has a top surface 774 with contacts or otherconductive elements electrically connected to the internal components778, and has a bottom surface 777 facing in the opposite direction fromtop 774. In this embodiment, however, the orientation of the secondmicroelectronic element is the reverse of that discussed above. Thus,the top surface 774 of the second microelectronic element facesrearwardly with respect to the composite chip and thus faces away fromthe floor surface 738 of cavity 736. The contacts 776 of the secondmicroelectronic element are connected to additional conductive elements733 provided in a layer overlying the surface of the encapsulant 736 andoverlying the rear surface 726 of the body. Some of these additionalconductive elements may form interconnection or redistribution tracesextending between the contacts of the second microelectronic element andthe via conductors 712, so as to provide electrical interconnectionbetween the elements within layer 702. Some or all of the additionalconductive elements 733 may form further terminals 735. Terminals 735,as well as pads or terminals 713, desirably are adapted forsurface-mounting of the structure to a circuit panel such as a circuitboard. For example, these terminals may be provided with masses of anelectrically conductive bonding material such as a solder. The assemblymay further include a passivation layer 739 overlying the rear surface726 of the body, and overlying the encapsulant within cavity 736 and thesecond microelectronic element 770. The additional conductive features733 may be disposed within or on this passivation layer. Here again, thecavity 736, as well as vias 710, can be formed while body 722 is part ofa larger wafer, either before or after bonding semiconductor layer 702to the body. The body and the encapsulant within the cavity 736 can betreated to form a generally planar surface, and conductive features 712,733, and 735 can be formed on this planar surface or on a passivationlayer applied to the planar surface. While essentially any techniqueusable for forming conductive features can be used, non-lithographictechniques as discussed in greater detail in the co-pending applicationentitled Non-Lithographic Formation of Three-Dimensional ConductiveElements, filed of even date herewith, can be employed. Suchnon-lithographic techniques can include, for example, selectivelytreating a surface with a laser or with mechanical processes such asmilling or sandblasting so as to treat those portions of the surfacealong the path where the conductive element is to be formed differentlythan other portions of the surface. For example, a laser or mechanicalprocess may be used to ablate or remove a material such as a sacrificiallayer from the surface only along a and thus form a groove extendingalong the path. A material such as a catalyst can then be deposited inthe groove, and one or more metallic layers can be deposited in thegroove.

The structure of FIG. 13 includes an array of microlenses 791 and anarray of color filters 793 overlying the front surface 710 of layer 702in alignment with the photosensitive elements 728 of the layer. In theconventional manner, these structures modify the light impinging on thephotosensitive elements so as to allow formation of image datarepresenting a color image. A transparent cover 795 overlies themicrolenses and filters. The cover may be supported above the frontsurface 710 of layer 702 by a frame or spacer element 797 bonded betweenthe cover and the front surface 710. The cover may be fabricated andapplied on a wafer scale, before severance of the wafers to form theindividual unit depicted in FIG. 13. Also, the cover may include a lensor other optical elements (not shown) for use in forming the image. Thestructure of FIG. 13 thus provides a unitary, compact image-sensing andprocessing assembly. Merely by way of example, second chip 770 mayreceive raw data constituting an image from layer 702 and process theraw data before the data is transferred through the electricalconnections to other components of a circuit.

The various features discussed above can be combined with one another.For example, the floor surface and top surface redistribution conductors405 and 415, discussed above with reference to FIGS. 8-10, can be usedto make connections with terminals on the rear surface of the first chipor on the encapsulant surface, regardless of whether the structure hasvias extending through the walls bounding the cavities as shown in FIG.10. Also, the vias 402 in the walls of the first chip may be providedwith or without vias 448 extending between the cavity floor surface 438and the front surface 424 of the first chip, and with or without viasextending between the front and rear surfaces of the second chip.

The orientation of the second microelectronic element or second chip 770shown in FIG. 13 may be reversed, so that the top surface of the secondchip faces forwardly, toward the floor surface of cavity 736. The cavity736 in the carrier may be provided with floor surface and rearwardredistribution conductors as discussed above with reference to FIGS. 8and 9 or with vias in the encapsulant as shown in FIG. 11. Alternativelyor additionally, the second chip can have internal vias as depicted inFIG. 7. Conversely, in the structures discussed above with reference toFIGS. 1-12, the orientation of the second microelectronic element can bereversed so that the top surface of the second microelectronic elementfaces rearwardly with respect to the first chip. In a structure such asthat of FIG. 1, where the bottom surface of a second chip is exposed,the second chip may include photosensitive elements in an active layernear the top surface, and may be thinned to such a degree that lightimpinging on the bottom surface of the second chip will reach thesephotosensitive elements.

The particular via structure, with a single via conductor extendingwithin each via and surrounded by a via liner 59 (FIG. 1), can bereplaced by other structures. For example, some or all of the viasdiscussed above may be “many-to-one” vias. Each such via incorporates afirst section 850 (FIG. 14) of relatively large diameter and multiplesecond sections 852 of relatively small diameter. Such a via may havemultiple conductors, each including a section 853 within one of thesmall diameter second sections 852 of the via and a further section 854extending through the first section 850. The conductor sections 854 maybe formed as traces extending along the via walls or along a dielectriclayer (not shown) disposed on the via wall. The traces may be curved orzig-zag so that each trace has a length, as measured along the trace,longer than a theoretical straight line 859 extending along the wall ofthe via. As discussed in greater detail in the co-pending applicationsmentioned above, such curved or zig-zag traces help to reduce stressesin the traces which may otherwise be caused by differential thermalexpansion of the semiconductor material forming the walls of the via andthe metal constituting the trace. In a similar fashion, the rearwardredistribution conductors 407 extending along the sloping walls of thecavity (FIGS. 8 and 9) may be curved or zig-zagged to minimize stressesin these conductors. The curved or zig-zag conductors or traces can beformed, for example, using the non-lithographic processes discussedabove to define a curved or zig-zag path.

The structures discussed above provide extraordinary three-dimensionalinterconnection capabilities. These capabilities can be used with chipsof any type. Merely by way of example, the following combinations ofchips can be included in structures as discussed above: (i) a processorand memory used with the processor; (ii) plural memory chips of the sametype; (iii) plural memory chips of diverse types, such as DRAM and SRAM;(iv) an image sensor and an image processor used to process the imagefrom the sensor; (v) an application-specific integrated circuit (“ASIC”)and memory.

The structures discussed above can be utilized in construction ofdiverse electronic systems. For example, a system 900 in accordance witha further embodiment of the invention includes a structure 906 asdescribed above in conjunction with other electronic components 908 and910. In the example depicted, component 908 is a semiconductor chipwhereas component 910 is a display screen, but any other components canbe used. Of course, although only two additional components are depictedin FIG. 15 for clarity of illustration, the system may include anynumber of such components. The structure 906 as described above may be,for example, a composite chip as discussed above in connection with FIG.13, or a structure incorporating plural chips as discussed withreference to FIGS. 1-12. In a further variant, both may be provided, andany number of such structures may be used. Structure 906 and components908 and 910 are mounted in a common housing 901, schematically depictedin broken lines, and are electrically interconnected with one another asnecessary to form the desired circuit. In the exemplary system shown,the system includes a circuit panel 902 such as a flexible printedcircuit board, and the circuit panel includes numerous conductors 904,of which only one is depicted in FIG. 15, interconnecting the componentswith one another. However, this is merely exemplary; any suitablestructure for making electrical connections can be used. The housing 901is depicted as a portable housing of the type usable, for example, in acellular telephone or personal digital assistant, and screen 910 isexposed at the surface of the housing. Where structure 906 includes alight-sensitive element such as an imaging chip, a lens 911 or otheroptical device also may be provided for routing light to the structure.Again, the simplified system shown in FIG. 15 is merely exemplary; othersystems, including systems commonly regarded as fixed structures, suchas desktop computers, routers and the like can be made using thestructures discussed above.

As these and other variations and combinations of the features discussedabove can be utilized without departing from the present invention, theforegoing description of the preferred embodiments should be taken byway of illustration rather than by way of limitation of the invention asdefined by the claims.

The invention claimed is:
 1. A microelectronic structure comprising: (a)a first semiconductor chip having a body with oppositely-facing frontand rear surfaces, and a cavity extending into the body from the rearsurface, the first chip having active circuit elements integral with thebody disposed in an active layer adjacent the front surface, and (b) anadditional microelectronic element disposed within the cavity, thestructure defining a substantially planar structure rear surfaceincluding the rear surface of the first semiconductor chip; and (c)terminals carried on the front surface of the first semiconductor chip,the microelectronic structure being constructed and arranged so that themicroelectronic structure including the first semiconductor chip and theadditional microelectronic element can be mounted to a circuit panel bybonding the terminals to a circuit panel.
 2. A microelectronic structureas claimed in claim 1 wherein the first chip has a rearwardly-facingcavity floor surface within the cavity and a wall bounding the cavityand projecting rearwardly from the cavity floor surface to the rearsurface of the first semiconductor chip.
 3. A microelectronic structureas claimed in claim 2 wherein the wall and rear surface bound the cavityon at least two opposite sides of the cavity.
 4. A microelectronicstructure as claimed in claim 3 wherein the wall and rear surfaceentirely surround the cavity.
 5. A microelectronic structure as claimedin claim 3 wherein the cavity occupies at least 25% of the area of thechip.
 6. A microelectronic structure as claimed in claim 2 wherein theadditional microelectronic element has a front surface disposed withinthe cavity of the first chip and facing toward the floor surface, andwherein the additional microelectronic element has electrical contactsexposed at the front surface.
 7. A microelectronic structure as claimedin claim 2 further comprising electrically conductive via conductorsextending forwardly into the first chip from the floor surface of thecavity, at least some of the via conductors being electrically connectedto the contacts of the additional microelectronic element.
 8. Amicroelectronic structure as claimed in claim 7 wherein at least some ofthe active circuit elements in the active layer of the first chipoverlie the cavity, at least some of the via conductors extendingbetween the active circuit elements.
 9. A microelectronic structure asclaimed in claim 1 wherein the additional microelectronic element is asecond semiconductor chip.
 10. A microelectronic structure as claimed inclaim 1 further comprising a dielectric encapsulant within the cavity atleast partially surrounding the additional microelectronic element. 11.A microelectronic structure as claimed in claim 10 wherein theencapsulant defines a portion of the structure rear surface.
 12. Amicroelectronic structure as claimed in claim 1 wherein a bottom surfaceof the additional microelectronic element defines a portion of thestructure rear surface.
 13. A microelectronic structure comprising: (a)a first semiconductor chip having a crystalline body withoppositely-facing front and rear surfaces, and a cavity extending intothe body from the rear surface, the cavity having a rearwardly-facingcavity floor surface; the first chip having vias extending forwardlyinto the first chip from the floor surface of the cavity, the first chiphaving active circuit elements integral with the body disposed in anactive layer adjacent the front surface; at least some of the activecircuit elements overlying the cavity, at least some of the viasextending through the active layer between active circuit elements, thefirst chip further having electrically conductive via conductorsdisposed in the vias; and (b) an additional microelectronic elementdisposed at least partially within the cavity of the first chip, theadditional microelectronic element being electrically connected to atleast some of the via conductors.
 14. A microelectronic structure asclaimed in claim 13 wherein the vias have first portions adjacent thecavity floor surface and second portions remote from the cavity floorsurface, the second portions being of smaller diameter than the firstportions, the second portions extending through the active layer.
 15. Amicroelectronic structure as claimed in claim 14 wherein the additionalmicroelectronic element is connected to at least some of the activecircuit elements of the first chip by at least some of the viaconductors.
 16. A microelectronic structure as claimed in claim 14wherein the second portions of the vias have diameters of about 50 μm orless.
 17. A microelectronic structure as claimed in claim 14 wherein thefirst chip includes liners within the vias surrounding the viaconductors, the liners having a modulus of elasticity less than amodulus of elasticity of the via conductors and less than a modulus ofelasticity of the body.
 18. A microelectronic structure as claimed inclaim 13 wherein the first chip has electrically conductive terminalsexposed at the front surface and wherein the additional microelectronicelement is connected to at least some of the terminals by at least someof the via conductors.
 19. A microelectronic structure as claimed inclaim 14 wherein the additional microelectronic element has a topsurface facing toward the cavity floor surface and top contacts exposedat the top surface, at least some of the top contacts being electricallyconnected to at least some of the via conductors.
 20. A structure asclaimed in claim 19 further comprising redistribution traces extendingalong at least one of the cavity floor surface and the top surface, atleast some of the top contacts being electrically connected to at leastsome of the via conductors through at least some of the redistributiontraces.
 21. A structure as claimed in claim 20 wherein theredistribution traces include cavity floor redistribution tracesextending predominantly in a first direction along the cavity floorsurface and top surface redistribution traces extending along the topsurface predominantly in a second direction transverse to the firstdirection.
 22. A structure as claimed in claim 17 wherein the body has arearwardly-facing cavity floor surface within the cavity and a wallbounding the cavity and projecting rearwardly from the cavity floorsurface to the rear surface of the body.
 23. A structure as claimed inclaim 22 wherein the wall and rear surface bound the cavity on at leasttwo opposite sides of the cavity.
 24. A structure as claimed in claim 23wherein the wall and rear surface entirely surround the cavity.
 25. Astructure as claimed in claim 23 wherein the cavity occupies at least25% of the area of the body.
 26. A structure as claimed in claim 22wherein said additional microelectronic element is electricallyconnected to at least some of the active circuit elements of the firstcomposite chip.
 27. A structure as claimed in claim 22 wherein theadditional microelectronic element has a bottom surface disposed withinthe cavity of the first chip and facing toward the cavity floor surface,a top surface facing in the same direction as the rear surface of thebody, and contacts exposed at the top surface, at least some of thecontacts being connected to at least some of the via conductors.
 28. Asystem comprising a structure according to any one of claims 1 and 13and one or more other electronic components electrically connected tothe structure.
 29. A system as claimed in claim 28 further comprising ahousing, said structure and said other electronic components beingmounted to said housing.